Use of nucleating agents to increase the flexural modulus of ionomers

ABSTRACT

A golf ball composition having a copolymer with an acid content modified by a nucleating agent is described. The nucleating agent modifies the flexural modulus of the acid copolymer.

FIELD OF THE INVENTION

The present invention generally relates to ionomers modified withnucleating agents to improve flexural modulus.

BACKGROUND OF THE INVENTION

Ionomeric resins are copolymers containing non-ionic repeating units andsmaller amounts of ion containing units. Various ionomeric resins andblends thereof (sold by E. I. DuPont de Nemours & Company under thetrademark Surlyn®, and by the Exxon Corporation under the trademarksEscor® and Iotek®, among others) have been used as golf ball covers.Ionomer covers are generally more durable than the traditional “balata”(trans polyisoprene, natural, or synthetic) rubber covers. The softerbalata covers, although exhibiting enhanced playability properties, lackthe durability properties required for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin, such asethylene, and a metal salt of an unsaturated carboxylic acid, such asacrylic acid, methacrylic acid, or maleic acid. In some instances, anadditional softening monomer, such as an acrylate, can also be includedto form a terpolymer. The pendent ionic groups in the ionomeric resinsinteract to form ion-rich aggregates contained in a non-polar polymermatrix. The metal ions, such as sodium, zinc, magnesium, lithium,potassium, calcium, nickel, manganese, copper, titanium, aluminum etc.are used to neutralize some portion of the acid groups in the copolymer,resulting in a thermoplastic elastomer exhibiting enhanced properties,i.e. improved durability, etc.

The ionomeric resins utilized to produce cover compositions can beformulated according to known procedures such as those set forth in U.S.Pat. No. 3,421,766 or British patent no. 963,380, with neutralizationeffected according to procedures disclosed in Canadian patent nos.674,595 and 713,631, wherein the ionomer is produced by copolymerizingthe olefin and carboxylic acid to produce a copolymer having the acidunits randomly distributed along the polymer chain. Ionic copolymersgenerally comprise one or more α-olefins, and from about 9 to about 20weight percent of α,β-ethylenically unsaturated mono- or dicarboxylicacid. The base copolymer is neutralized with metal ions to the extentdesired.

The ionomeric resins utilized in the golf ball industry are generallycopolymers of ethylene with acrylic (e.g. Escor®) and/or methacrylic(e.g. Surlyn®) acid. In addition, two or more types of ionomeric resinsmay be blended into the cover compositions in order to produce thedesired properties of the resulting golf balls. Generally, ionomers inthe mid-acid range have lower flexural modulus than the high-acidionomers, and high acid ionomers also tend to be more brittle or lessdurable than mid-acid ionomers. However, the mid-acid ionomers aregenerally less expensive. Higher flexural modulus materials when used asan inner cover layer or outer cover layer reduce spin and increasecoefficient of restitution at high swing speeds. Hence, there remains aneed to modify mid-acid ionomers to increase flexural modulus.

SUMMARY OF THE INVENTION

The present invention relates to a golf ball that includes an ionomercomposition modified to increase its flexural modulus.

The present invention also relates to a golf ball having an ionomercomposition modified with at least one nucleating agent.

It is understood that both the forgoing general description and thefollowing detailed description are exemplary and explanatory only, andare intended to provide a further explanation of the present invention,as claimed.

DETAILED DESCRIPTION OF THE INVENTION

“Copolymer” means polymers containing two or more different monomers.The terms “dipolymer” and “terpolymer” mean polymers containing only twoand three different monomers respectively. The phrase “copolymer ofvarious monomers” means a copolymer whose units are derived from thevarious monomers.

Flexural modulus is the ratio of stress to strain within the elasticlimit (when measured in the flexural mode) and is similar to tensilemodulus. This property is used to indicate the bending stiffness of amaterial. The flexural modulus, which is a modulus of elasticity, isdetermined by calculating the slope of the linear portion of thestress-strain curve during the bending test. The formula used tocalculate the flexural modulus from the recorded load (F) and deflection(D) is: $E_{B} = {\frac{3}{4}\frac{{FL}^{3}}{{bd}^{\quad 3}D}}$

Wherein

L=span of specimen between supports (m);

b=width (m); and

d=thickness (m).

Flexural modulus can be determined or measured in accordance to ASTMD790 standard, among other protocols.

An ionomer is a thermoplastic polymer which includes acidic groups, suchas carboxylate or sulfonate, or basic groups, such as quaternarynitrogen, the acidic or basic groups being at least partiallyneutralized with a conjugate acid or base. Negatively charged acidicgroups, such as carboxylate or sulfonate, may be neutralized with acation, such as a metal ion. Positively charged basic groups, such asquaternary nitrogen, may be neutralized with an anion, such as a halide,an organic acid, or an organic halide. Acidic or basic groups may beincorporated into an ionomer through copolymerization of an acidic orbasic monomer, such as alkyl (meth)acrylate, with at least one othermonomer, such as an olefin, styrene or vinyl acetate, followed by atleast partial neutralization to form an ionomer. Alternatively, acidicor basic groups may be incorporated into a polymer to form an ionomer byreacting the polymer, such as polystyrene or a polystyrene copolymerincluding a block copolymer of polystyrene, with a functionalizingreagent, such as a carboxylic acid or sulfonic acid, followed by atleast partial neutralization. Suitable metal ions include sodium, zinc,magnesium, lithium, potassium, calcium, nickel, manganese, copper,titanium, aluminum and etc.

Chemically, ionomer resins are a copolymer of an olefin and an alpha,beta ethylenically-unsaturated carboxylic acid having 10-90% of thecarboxylic acid groups neutralized by a metal ion. See U.S. Pat. No.3,264,272. Commercially available ionomer resins include, for example,copolymers of ethylene and methacrylic or acrylic acid neutralized withmetal salts. These are sold by E. I. DuPont de Nemours and Co. under thetrademark SURLYN® and by the Exxon Corporation under the trademarkESCOR® and the trademark IOTEK®. These ionomer resins are distinguishedby the type of metal ion, the amount of acid, and the degree ofneutralization.

The term “(meth)acrylate” refers to acrylic and/or methacrylic, forexample, acrylic acid and/or methacrylic acid, or alkyl acrylate and/oralkyl methacrylate. In this connection, “ethylene/(meth)acrylic acid(abbreviated E/(M)AA)” means a copolymer of ethylene (abbreviatedE)/acrylic acid (abbreviated AA) and/or methacrylic acid (abbreviatedMAA), which can then be at least partially neutralized by one or morealkali metal, transition metal, or alkaline earth metal cations to forman ionomer.

The composition of the golf ball of the present invention includes atleast a copolymer that includes a low to medium acid content, generallyless than about 16% weight of acid, and a nucleating agent.Alternatively, the composition of the golf ball includes at least acopolymer that includes a high acid content, generally more than about16% weight of acid, preferably from about 17% to about 25% by weight ofa carboxylic acid, more preferably from about 18.5% to about 21.5% byweight of a carboxylic acid, and a nucleating agent. The composition ofthe present invention may be incorporated in forming the core, anyintermediate layers, and/or the cover layer of the golf ball.Preferably, the composition of the present invention is incorporated informing the intermediate or cover layer of the golf ball.

The copolymer of the present invention is a copolymer of a-olefin, C₃ toC8 α,β-ethylenically unsaturated carboxylic acid and optional softeningmonomer, which is prepared by methods known to one skilled in the art.Copolymers may include, without limitation, ethylene acid copolymers,such as ethylene/(meth)acrylic acid, ethylene/(meth)acrylic acid/maleicanhydride, ethylene/(meth)acrylic acid/maleic acid mono-ester,ethylene/maleic acid, ethylene/maleic acid mono-ester,ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike.

Preferably, the copolymer is an ionomeric resin. Ionomers for use in theinvention may include melt-processible, at least partially neutralizedcopolymers of ethylene and C₃ to C₈ α,β-ethylenically unsaturatedcarboxylic acids. Preferred ionomers for use in the present inventioninclude E/(M)AA dipolymers having from about 2 to about 30 weight %(M)AA, at least partially neutralized by one or more alkali metal,transition metal, or alkaline earth metal cations. More preferably, theionomer of the present invention includes E/(M)AA di-polymers having lowto medium acid content. U.S. patent application publication no.2005/0020741, which is incorporated herein by reference in its entirety,provides a list of copolymers that may be used in the present invention.The ionomer may contain from about 1 to about 99 wt. % neutralizedcopolymers of ethylene and C₃ to C₈ α,β-ethylenically unsaturatedcarboxylic acids, and from about 1 to about 99 wt. %ethylene/(meth)acrylic acid.

Optionally, the ionomeric composition of the present invention includesa non-ionomeric thermoplastic polymer. Suitable non-ionomericthermoplastic resins include, without limitation, thermoplasticelastomers, such as polyurethane, poly-ether-ester, poly-amide-ether,polyether-urea, Pebax™ (a family of block copolymers based onpolyether-block-amide, commercially supplied by Atochem of Philadelphia,Pa.), styrene-butadiene-styrene (SBS) block copolymers,styrene-(ethylene-butylene)-styrene block copolymers, etc., polyamide(oligomeric and polymeric), polyesters, polyolefins includingpolyethylene, polypropylene, ethylene/propylene copolymers, etc.,ethylene copolymers with various comonomers, such as vinyl acetate,(meth)acrylates, (meth)acrylic acid, epoxy-functionalized monomers, CO,etc., polycarbonates, acrylics, such as methyl methacrylate homopolymersor copolymers, polystyrene, polymers functionalized with maleicanhydride, epoxidization etc., either by copolymerization or bygrafting, elastomers such as EPDM, metallocene catalyzed PE andcopolymer, ground-up powders of the thermoset elastomers, etc.

Any method known to one skilled in the art may be used to make theionomers of the present invention. Some exemplary methods for makingionomers are described in U.S. Pat. No. 3,262,272, which is incorporatedherein by reference in its entirety. Ionomers with any acid content canbe used in the present invention. Preferably, the ionomers of thepresent invention are low to medium acid ionomers. In general, ioniccopolymers including up to about 16 percent acid are considered “low tomedium acid” ionomers, while those including greater than about 16percent acid are considered “high acid” ionomers. Examples of suitablelow to medium acid ionomers include medium acid Surlyns®, such asSurlyn® 7940 and Surlyn® 8940, Escor® 4000/7030 and Escor® 900/8000.Escor® 4000/7030 and Escor® 900/8000 are described in U.S. Pat. Nos.4,911,451 and 4,884,814, which are incorporated herein by reference intheir entireties. Two or more ionomers can be blended to form the basepolymer.

In the present invention, one or more nucleating agents are added to theionomers, preferably, low to mid-acid ionomers. However, nucleatingagents can also be added to high acid ionomers. Examples of the highacid methacrylic acid based ionomers found suitable for use inaccordance with this invention include, but are not limited to, SURLYN8220 and 8240 (both formerly known as forms of SURLYN AD-8422), SURLYN9220 (zinc cation), SURLYN SEP-503-1 (zinc cation), and SURLYN SEP-503-2(magnesium cation). According to DuPont, all of these ionomers containfrom about 18.5 to about 21.5% by weight methacrylic acid. Examples ofthe high acid acrylic acid based ionomers suitable for use in thepresent invention also include, but are not limited to, the high acidethylene acrylic acid ionomers produced by Exxon such as Ex 1001, 1002,959, 960, 989, 990, 1003, 1004, 993, and 994, and Surlyn 6120(Mg), 8140,8150(Na), 9120 and 9150(Zn). The nucleating agents may be added to theionomers in any number of ways known to one skilled in the art.Preferably, the nucleating agents are capable of modifying theproperties of the ionomers, which are not amorphous by changing theirsemicrystalline nature, such as their degree of crystallinity and thedistribution of crystallite sizes. Without being bound by any particulartheory, typically a nucleating agent leads to greater uniformity in therate of crystal growth and in the size, number, and type of crystalsformed from the molten ionomer of the present invention. The moreuniform crystalline texture produced by the added nucleating agent mayresult in increased flexural modulus.

The nucleating agent of is capable of increasing the flex modulus of thebase ionomeric resin by up to about 10%, or more. In one example of thepresent invention, the nucleating agent of the present invention iscapable of modifying the flexural modulus of a 15% acid ionomer blend tohave the flexural modulus of a 19% acid ionomer blend.

Various nucleating agents can be incorporated into the composition ofthe present invention. The nucleating agent is added to the ionomericresins in an amount sufficient to provide the desired modification ofthe crystal structure. Suitable nucleating agents include, but are notlimited to, mineral nucleating agents and organic nucleating agents.Examples of mineral nucleating agents include, but are not limited to,carbon black, silica, kaolin, and talc. The organic nucleating agentsinclude, but are not limited to, salts of aliphatic mono-basic ordi-basic acids or aryl/alkyl acids such as sodium succinate, sodiumglutarate, sodium caproate, sodium 4-methylvalerate, aluminum phenylacetate, and sodium cinnamate. Alkali metal and aluminum salts ofaromatic and alicyclic carboxylic acids such as aluminum benzoate,sodium or potassium benzoate, sodium betanaphtholate, lithium benzoate,and aluminum tertiary-butyl benzoate also are suitable organicnucleating agents. Substituted sorbitol derivatives, such as bis(benzylidene) and bis (alkylbenzilidine) sorbitols, wherein the alkylgroups contain from about 2 to about 18 carbon atoms, are also suitablenucleating agents.

Preferably, suitable nucleating agents of the present invention include,but are not limited to, 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol,c-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid, disodium salt,and/or amorphous silicon dioxide, 13-docosenamide (Z). Additionally,sorbitol derivatives such as 1,3,2,4-dibenzylidene sorbitol,1,3,2,4-di-para-methylbenzylidene sorbitol, and1,3,2,4-di-para-methylben-zylidene sorbitol are effective nucleatingagents for polypropylenes. 1,2:2,4 bis(3,4-dimethylbenzylidene) sorbitolnucleating agent is commercially available, as Millad® 3988 fromMilliken Chemical Co. C-endobicyclo[2,2.1]heptane-2,3-dicarboxylic acidnucleating agent is commercially available as HPN 68-L, also fromMilliken. U.S. patent application Ser. No. 10/852,345, which isincorporated herein by reference in its entirety, provides severalexamples of nucleating agent that may be used in the present invention.The amount of nucleating agent incorporated into the composition of thepresent invention generally range from about 0.05% to about 0.25% of thecomposition. Preferably the amount of nucleating agent is from about0.05% to about 0.15%. Preferably, the nucleating agent such as Millad®3988 is in a powder form having a size of at least about 38 μm and hasdensity in the range of about 725 kg/m³.

An optional filler may be included in the thermoplastic composition ofthe present invention, e.g. to impart additional density to the ionomersor blends thereof with other materials. Preferred densities for thefilled compositions include densities in the range starting with thedensity of unfilled polymer to about 1.8 gm/cc. Generally, the fillerwill be an inorganic material, having a density greater than about 4gm/cc, preferably greater than 5 gm/cc, and is present in an amount offrom about 0 to about 60 weight % based on the total weight of thecomposition. Examples of useful fillers include zinc oxide, bariumsulfate, lead silicate and tungsten carbide, tin oxide, as well as theother well known corresponding salts and oxides thereof. It is preferredthat the filler materials be non-reactive or almost non-reactive withthe polymer components described above when the ionomers are less thancompletely neutralized. If the ionomers are fully neutralized, reactivefillers may be used. Zinc oxide grades, such as grade XX503R, areavailable from Zinc Corporation of America of Monaca, Pa., which do notreact readily with any free acid to cause cross-linking.

Other additives suitable for use in the present invention include butare not limited to, titanium dioxide, which may be used as a whiteningagent or filler, other pigments, optical brighteners, surfactants,processing aids, or the like.

EXAMPLES

The following examples and comparative examples further illustrate thepresent invention in detail, but are not to be construed to limit thescope of the present invention.

A 50/50 blend of Surlyn® 7940 and Surlyn® 8940 were blended together toform the base polymer. As illustrated in Table 1, below, nucleatingagent Millad® 3988 was added to blends 1, 2, and 3 in an amount of0.05%, 0.1%, and 0.15%, respectively. Furthermore, as illustrated inTable 1, nucleating agent HPN® 68-L was added to blends 4, 5, and 6 inan amount of 0.05%, 0.1%, and 0.15%, respectively. The results areillustrated in Table 1 below: TABLE 1 Composition Components Blend 1Blend 2 Blend 3 Blend 4 Blend 5 Blend 6 Control Surlyn ® 7940 ionomer50% 50% 50% 50% 50% 50% 50% Surlyn ® 8940 ionomer 50% 50% 50% 50% 50%50% 50% Millad ® 3988 nucleating agent 0.05%   0.1%  0.15%    0% HPN ®68-L nucleating agent 0.05%   0.1%  0.15%    0% Flex Modulus @40 hrs,ksi 60.2 59 51.1 53.4 59.1 54.5 51.3 Flex Modulus @2 wks, ksi 77 72.571.5 69.5 74.1 71.5 70.2

As illustrated in Table 1 above, the control had a 50/50 blend ofionomers Surlyn® 7940 and Surlyn® 9840 without any nucleating agents.This blend resulted in having a flexural modulus of 51.3 ksi at 40 hoursand a flexural modulus of 70.2 ksi at two weeks.

In comparison, Blends 1, 2, and 3, in addition to having a 50/50 blendof ionomers Surlyn® 7940 and Surlyn® 9840, included 0.05%, 0.1%, and0.15% of the nucleating agent Millad® 3988, respectively. The flexuralmodulus of Blend 1 at 40 hours was 60.2 ksi and at two weeks was 77 ksi,which are about 17% and 9.7% higher than the flexural modulus of thecontrol at 40 hours and at two weeks, respectively. With respect toBlend 2, the flexural modulus at 40 hours was 59 ksi and at two weekswas 72.5 ksi, which are about 15% and 3.3% higher than the flexuralmodulus of the control at 40 hours and at two weeks, respectively.Flexural modulus of Blend 3 at 40 hours was 51.1 ksi and at two weekswas 71.5 ksi, which are about the same within measurement uncertaintyand 1.9% higher than the flexural modulus of the control at 40 hours andat two weeks, respectively.

Blends 4, 5, and 6, in addition to having a 50/50 blend of ionomersSurlyn® 7940 and Surlyn® 9840, included 0.05%, 0.1%, and 0.15% of thenucleating agent HPN® 68-L, respectively. The flexural modulus of Blend4 at 40 hours was 53.4 ksi and at two weeks was 69.5 ksi, which areabout 4.1% higher and 1% lower or within measurement uncertainty thanthe flexural modulus of the control at 40 hours and at two weeks,respectively. With respect to Blend 5, the flexural modulus at 40 hourswas 59.1 ksi and at two weeks was 74.1 ksi, which are about 15.2% and5.5% higher than the flexural modulus of the control at 40 hours and attwo weeks, respectively. Flexural modulus of Blend 6 at 40 hours was54.5 ksi and at two weeks was 71.5 ksi, which are about 6.2% and 1.9%higher than the flexural modulus of the control at 40 hours and at twoweeks, respectively.

While two ionomer blends are represented in the examples, the presentinvention is not limited thereto. One ionomer systems and three or moreionomer systems can also be used. Other non-ionomeric polymers can alsobe included.

Other than in the operating examples, or unless otherwise expresslyspecified, all of the numerical ranges, amounts, values and percentages,such as those for amounts of materials and others in the specification,may be read as if prefaced by the word “about”, even though the term“about” may not expressly appear with the value, amount or range.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and attached claims are approximationsthat may vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges ofvarying scope are set forth herein, it is contemplated that anycombination of these values inclusive of the recited values may be used.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalent thereof.

1. A golf ball comprising a core, a cover layer, and optionally at leastone intermediate layer disposed between the core and the cover layer,wherein at least one portion of the ball comprises an ionomercomposition modified with a nucleating agent.
 2. The golf ball of claim1, wherein the copolymer has an acid content of from about 5% to about25% by weight.
 3. The golf ball of claim 1, wherein the copolymer has anacid content of less that 16% by weight.
 4. The golf ball of claim 1,wherein the ionomer composition is partially or fully neutralized withmetal ions.
 5. The golf ball of claim 4, wherein the metal ions compriseZn, Na, Li, K, Ca, Mg, Ni, Mn, Cu, Ti, Al, or a combination thereof. 6.The golf ball of claim 1, wherein the nucleating agent is capable ofincreasing the flexural modulus of the ionomer composition.
 7. The golfball of claim 1, wherein the nucleating agent comprises1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol,c-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid, disodium salt,amorphous silicon dioxide, 13-docosenamide (Z), or a combinationthereof.
 8. The golf ball of claim 1, wherein the nucleating agentcomprises mineral nucleating agent, organic nucleating agent, alkalimetal and aluminum salt of aromatic and alicyclic carboxylic acid,substituted sorbitol derivative, sorbitol derivative, or a combinationthereof.
 9. The golf ball of claim 8, wherein the mineral nucleatingagent includes carbon black, silica, kaolin, talc, or a combinationthereof.
 10. The golf ball of claim 8, wherein the organic nucleatingagent includes salt of aliphatic mono-basic, a di-basic acid or anaryl/alkyl acid.
 11. The golf ball of claim 8, wherein the organicnucleating agent comprises sodium succinate, sodium glutarate, sodiumcaproate, sodium 4-methylvalerate, aluminum phenyl acetate, sodiumcinnamate, or a combination thereof.
 12. The golf ball of claim 8,wherein the alkali metal and aluminum salt of aromatic and alicycliccarboxylic acids include an aluminum benzoate, sodium or potassiumbenzoate, sodium betanaphtholate, lithium benzoate, aluminumtertiary-butyl benzoate, or a combination thereof.
 13. The golf ball ofclaim 8, wherein the substituted sorbitol derivative includes bis(benzylidene) and bis (alkylbenzilidine) sorbitols, wherein the alkylgroup of alkylbenzilidine includes from about 2 to about 18 carbonatoms.
 14. The golf ball of claim 8, wherein the sorbitol derivativeincludes 1,3,2,4-dibenzylidene sorbitol,1,3,2,4-di-para-methylbenzylidene sorbitol,1,3,2,4-di-para-methylben-zylidene sorbitol, or a combination thereof.15. The golf ball of claim 1, wherein the ionomer composition comprisesat least partially neutralized copolymers of ethylene and C₃ to C8α,β-ethylenically unsaturated carboxylic acids, ethylene/(meth)acrylicacid, or a combination thereof.
 16. The golf ball of claim 1, whereinthe ionomer composition comprises at least two ionomers.
 17. The golfball of claim 1, wherein the ionomer comprises from 1 to 99 wt. %neutralized copolymers of ethylene and C₃ to C₈ α,β-ethylenicallyunsaturated carboxylic acids, and from 1 to 99 wt. %ethylene/(meth)acrylic acid.
 18. The golf ball of claim 1, wherein thenucleating agent is in a powder form.